Fuel cell electrodes with conduction networks

ABSTRACT

A fuel cell electrode layer may include a catalyst, an electronic conductor, and an ionic conductor. Within the electrode layer are a plurality of electronic conductor rich networks and a plurality of ionic conductor rich networks that are interspersed with the electronic conductor rich networks. A volume ratio of the ionic conductor to the electronic conductor is greater in the ionic conductor rich networks than in the electronic conductor rich networks. During operation of a fuel cell that includes the electrode layer, conduction of electrons occurs predominantly within the electronic conductor rich networks and conduction of ions occurs predominantly within the ionic conductor rich networks.

FIELD OF THE INVENTION

The present disclosure relates generally to fuel cells and/or fuel cellsubassemblies and methods for fabrication of fuel cells and/or fuel cellsubassemblies.

BACKGROUND

A fuel cell is an electrochemical device that combines hydrogen fuel andoxygen from the air to produce electricity, heat, and water. Fuel cellsdo not utilize combustion, and produce little if any hazardouseffluents. Fuel cells convert fuel gases directly into electricity, andcan be operated at much higher efficiencies than many other types ofelectric generators.

A typical polymer electrolyte membrane (PEM) fuel cell includes amembrane electrode assembly (MEA) comprising an ion conducting membrane(the PEM) with an anode electrode disposed on one side of the ionconducting membrane and a cathode electrode disposed on the other sideof the ion conducting membrane. Hydrogen is reduced into hydrogen ionsand electrons at the anode electrode. The electrons provide anelectrical current to drive an external load and the hydrogen ions passthrough the membrane. At the cathode electrode, oxygen combines with thehydrogen ions to form water as a byproduct. Fuel cell operation dependsin part on the degree of transportation of gases, liquids, electrons,and ions through the materials that form the layers of the MEA.

SUMMARY

Embodiments described in the disclosure involve a fuel cell electrodelayer that includes a catalyst, an electronic conductor, and an ionicconductor. Within the electrode layer are a plurality of electronicconductor rich networks and a plurality of ionic conductor rich networksthat are interspersed with the electronic conductor rich networks. Avolume ratio of the ionic conductor to the electronic conductor isgreater in the ionic conductor rich networks than in the electronicconductor rich networks. During operation of a fuel cell that includesthe electrode layer, conduction of electrons occurs predominantly withinthe electronic conductor rich networks and conduction of ions occurspredominantly within the ionic conductor rich networks.

In some implementations, the ionic conductor may include spray driedparticles of an ion conducting polymer. The ionic conducting polymer maycomprise perfluorinated sulfonic acid (PFSA), and/or perfluorinatedimide acid (PFIA), and/or a hydrocarbon, for example. Many particles,and in some embodiments a majority of the particles, may be hollowspheroids which have outer surfaces that are substantially smooth. Amajority of the particles may have diameters greater than 50 nm ordiameters in a range of about 1 μm to about 15 μm, for example.

In some implementations, the electronic conductor can be catalyst coatedelectronic conductor particles, e.g., platinum coated on carbon.Alternatively, the catalyst may be disposed on support elements otherthan the electronic conductor, such as nanostructured support elements.The electronic conductor may include one or more of carbon, tin oxide,and titanium oxide. The catalyst may be one or more of platinum,palladium, bimetals, metallic alloys, and carbon nanotubes. The solventmay comprise water, alcohol, and/or other hydrocarbons, for example.

The ionic conductor may comprise particles of a first ion conductingpolymer and the electrode layer may further include particles of asecond ion conducting polymer. According to some aspects, the first ionconducting polymer has a first equivalent weight and the second ionconducting polymer has a second equivalent weight. A majority of theparticles of the second ion conducting polymer may have diameters lessthan about 50 nm and a majority of the particles of the first ionconducting polymer may have diameters greater than about 50 nm orgreater than about 1 μm or have an average diameter of about 3.5 μm. Insome implementations, the particles of the second ion conducting polymerform a film on the electronic conductor and the particles of the firstion conducting polymer comprise a majority of the volume of the ionicconductor. The particles of the first ion conducting polymer havingdiameters greater than about 1 μm may substantially form the ionconducting networks.

The electrode layer may be disposed on a fuel cell electrolyte membraneor on a gas diffusion layer. The electrode layer can be disposed betweena first surface of a fuel cell electrolyte membrane and a first gasdiffusion layer that are components of a membrane electrode assembly(MEA). The MEA also includes a second electrode layer disposed between asecond surface of the electrolyte membrane and a second gas diffusionlayer. The second electrode layer may or may not include ionic andelectronic networks. The fuel cell subassembly may further include firstand second flow field plates positioned, respectively, proximate thefirst and second gas diffusion layers. Multiple MEAs may be arranged toform a fuel cell stack.

A method of making a fuel cell electrode layer includes combining anionic conductor, an electronic conductor, a catalyst, and a solvent toform an electrode ink. The ionic conductor comprises smooth, spheroidparticles, a majority of the particles having diameters greater thanabout 50 nm or greater than 1 μm, or in a range between about 50 nm toabout 15 μm, for example. The ionic conductor, the electronic conductor,the catalyst, and the solvent of the electrode ink are mixed for aperiod of time. The electrode ink is coated on a substrate and dries toform the fuel cell electrode layer.

In some electrode inks, the electronic conductor is coated with thecatalyst. Some electrode inks include catalyst which is disposed onsupport structures other than the electronic conductor. The supportstructures can be nanostructured supports, for example.

A fuel cell catalyst coated membrane (CCM) may be formed by coating theelectrode ink on a fuel cell electrolyte membrane. The electrode ink mayalternatively or additionally be coated on a fuel cell gas diffusionlayer.

In some implementations, the particles of the ionic conductor comprisespray dried ionomer particles that can be hollow, substantiallyspherical (spheroid), and/or can have substantially smooth outersurfaces.

The method may involve substantially contemporaneously combining theionic conductor, the electronic conductor, and the solvent prior to themixing.

The method may involve forming a pre-mixture that includes theelectronic conductor and the solvent and mixing the pre-mixture for aperiod of time. After mixing the pre-mixture, the ionic conductor isadded to the pre-mixture and the ionic conductor and pre-mixture aremixed for a period of time.

The method may involve adding a second type or second form of ionicconductor before and/or after mixing the ionic conductor, the electronicconductor, the catalyst, and the solvent.

In several variations, the electrode ink may include multiple types orforms of ionic conductors, including a first type of ion conductingpolymer and a second type of ion conducting polymer. The electrode inkmay include a first form and a second form of the same ionic conductor.The electrode ink may include a first ionic conductor having a firstequivalent weight and a second ionic conductor having a secondequivalent weight.

The ionic conductor can comprise particles of a first ion conductingpolymer, a majority of the particles of the first ion conducting polymerhaving diameters greater than about 1 μm. A majority of the particles ofthe second ion conducting polymer have diameters less than about 50 nm.

In some implementations, a volume of the first ion conducting polymer isgreater that a volume of the second ion conducting polymer.

During formation of the electrode layer, the particles of the second ionconducting polymer may coat particles of the electronic conductor.

The method further includes forming the ionic conductor by spray dryingan ion conducting polymer. An additive such as cerium and/or manganesecompounds may be added during the formation of the spray dried ionicconductor and/or at other times during the formation of the electrodeink.

Combining the components of the electrode layer may be accomplished byone or more of ball mixing, stirring, and sonication.

Some embodiments involve a fuel cell subassembly that includes anelectrode layer, comprising a catalyst, an electronic conductor, and anionic conductor intermixed with the electronic conductor and thecatalyst. The ionic conductor includes particles, and a majority of theparticles are spheroids having diameters greater than about 50 nm.

In some implementations, a majority of the particles of the ionicconductor have a substantially smooth outer surface and/or are hollowand/or have diameters in a range of about 1 μm to about 15 μm.

The electronic conductor may be a catalyst coated electronic conductorand/or the catalyst may be coated on supports other than the electronicconductor. The ionic conductor may be one or more of perfluorinatedsulfonic acid and perfluorinated imide acid.

The fuel cell subassembly may further include a second ionic conductorof a form or type that is different from the ionic conductor. Forexample, the first ionic conductor may have a first equivalent weightand the second ionic conductor may have a second equivalent weight. Asanother example, the second ionic conductor may comprise particles, anda majority of the particles of the second ionic conductor may havediameters less than about 50 nm.

The particles of the ionic conductor may be distributed non-uniformlywithin the electrode layer and the particle of the second ionicconductor may coat the electronic conductor.

The electrode layer can be disposed on a fuel cell electrolyte membraneand/or on a fuel cell gas diffusion layer. The electrode layer may beincorporated into a fuel cell membrane electrode assembly and/or into afuel cell stack.

A fuel cell subassembly includes an electrode layer that includes acatalyst, an electronic conductor, a first ionic conductor and a secondionic conductor that is different from the first ionic conductor. Thefirst ionic conductor and the second ionic conductor are intermixed witheach other, the electronic conductor, and the catalyst within theelectrode layer.

The first and second ionic conductors may be different types of ionicconductor or may be different forms of the same type of ionomer.Particles of the first ionic conductor may be larger than particles ofthe second ionic conductor. Particles of the smaller particled ionicconductor may form a film on the electronic conductor. For example, amajority of particles of the second ionic conductor may have diametersless than about 50 nm. Particles of the first ionic conductor may bepowdered spray dried particles or powdered cryoground particles.Particles of at least one of the ionic conductors, e.g., particles ofthe first ionic conductor, may be non-uniformly distributed within theelectrode layer.

The above summary is not intended to describe each embodiment or everyimplementation. A more complete understanding of various embodimentswill become apparent and appreciated by referring to the followingdetailed description and claims taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a typical fuel cell and the fuel cell's basic operation;

FIG. 2A is a cross section diagram of a fuel cell electrode in which theionic conductor material and the electronic conductor material isdistributed substantially uniformly;

FIG. 2B is a close up representation of a region of the fuel cellelectrode of FIG. 2A;

FIG. 2C is a depiction of an ionic/electronic conductor structure havingan electronic conductor which is surrounded by numerous small particlesof the ionic conductor;

FIG. 2D illustrates a cross section of an ionic/electronic conductorstructure, in which the ionic conductor forms a film surrounding acatalyst coated electronic conductor;

FIG. 2E is a cross section diagram of a fuel cell electrode thatcomprises two ionic conductors;

FIG. 2F is a close up representation of a region of the fuel cellelectrode of FIG. 2E;

FIG. 2G illustrates a cross section of electrode layer that includesmicron sized powdered ionic conductor particles;

FIG. 2H is a close up representation of a region of the fuel cellelectrode of FIG. 2G;

FIG. 2I illustrates a cross section of electrode layer that includesmultiple powdered ionic conductors;

FIG. 2J is a close up representation of a region of the fuel cellelectrode of FIG. 2I;

FIG. 3A is a cross section diagram of a fuel cell electrode thatincludes ionic and electronic conductor rich networks;

FIG. 3B is a close up representation of a region of the fuel cellelectrode of FIG. 3A;

FIG. 3C is a cross section diagram of a fuel cell electrode thatincludes two ionic conductors, at least one of the ionic conductorsforming ionic conductor rich networks;

FIG. 3D is a close up representation of a region of the fuel cellelectrode of FIG. 2C;

FIG. 4A is a flow diagram of a fuel cell electrode fabrication processthat includes combining and mixing an ionic conductor and electronicconductor;

FIG. 4B is a flow diagram of a fuel cell electrode fabrication processthat includes pre-mixing the electronic conductor with a solvent priorto combining the pre-mixture with an ionic conductor;

FIG. 5A is an optical image of a fuel cell electrode fabricated using asolution-based ionomer as the ionic conductor;

FIG. 5B is an optical image of a fuel cell electrode fabricated using apowder-based ionomer as the ionic conductor;

FIG. 6 is a scanning electron microscope (SEMS) image of an ionomerpowder formed by spray drying;

FIGS. 7A and 7B are scanning electron microscope (SEMS) images of anionomer powder formed by cryogrinding;

FIG. 8 shows comparative polarization performance results for MEAs withsolution-based ionomer electrodes and powder-based ionomer electrodes;

FIG. 9 compares MEA performance of solution-based ionomer electrodes andpowder-based ionomer electrodes at current densities of 1.2 A/cm² and1.5 A/cm²;

FIG. 10 provides a comparison of the electrochemical surface area ofsolution-based ionomer electrodes and powder-based ionomer electrodes;

FIG. 11 provides a comparison of the catalytic activity of electrodesformed using solution-based ionomer, cryoground powdered ionomer, spraydried powdered ionomer, and spray dried powdered ionomer with apremixture of electronic conductor and solvent;

FIG. 12 shows comparative polarization curves for electrodes formedusing solution-based ionomer, cryoground powdered ionomer, spray driedpowdered ionomer, and spray dried powdered ionomer with a premixture ofelectronic conductor and solvent; and

FIG. 13 shows MEA performance at a current density of 1.2 A/cm² forelectrodes formed using solution-based ionomer, cryoground powderedionomer, spray dried powdered ionomer, and spray dried powdered ionomerwith a premixture of electronic conductor and solvent.

Embodiments of the invention are amenable to various modifications andalternative forms and are shown and described by way of example in thedrawings and the specification. It is to be understood, however, thatthe intention is not to limit the invention to the particularembodiments described. On the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the scope ofthe invention as defined by the appended claims.

DESCRIPTION OF VARIOUS EMBODIMENTS

Some of the basic components of a polymer electrolyte membrane (PEM)fuel cell 110 (without subgaskets, gaskets, or seals) are depicted inFIG. 1. In operation, hydrogen fuel, H₂, is introduced into the anodeside of the fuel cell 110, passing over the first flow field plate 112and through the gas diffusion layer (GDL) 114. Oxygen, O₂, from the airflows through the second flow field plate 119 and through the second GDL118 at the cathode side of the fuel cell 110. The GDLs 114, 118 promoteair and hydrogen diffusion to the anode and cathode electrodes 115, 113,and aid in drawing end product water vapor and liquid away from theelectrodes 115, 113. A microporous layer (not shown) may be disposedbetween the GDLs 114, 118 and the electrodes 115, 113. The flow fieldplates 112, 119 typically include a pattern of flow channels designed todistribute reactant gases across the active area of the fuel cell.

At the anode electrode layer 115, the hydrogen fuel is separated intohydrogen ions (H⁺) and electrons (e⁻). The electrolyte membrane 116permits the hydrogen ions or protons and water to pass through theelectrolyte membrane 116 to the cathode electrode layer 113 of the fuelcell 110. The electrons flow through an external electrical circuit 117in the form of electric current. At the cathode electrode layer 113,oxygen, hydrogen ions, and electrons combine to produce water (H₂O) andheat. The electrical current produced by the fuel cell 110 can power anelectric load 117, such as an electric motor, and/or can be directed toan energy storage device, such as a rechargeable battery. Five layers ofthe fuel cell, the membrane 116, electrodes 113, 115, and GDLs 114, 118,are often referred to as a membrane electrode assembly (MEA).

Individual fuel cells, such as the fuel cell 110 shown in FIG. 1, can becombined with a number of other fuel cells to form a fuel cell stack.The number of fuel cells within the stack determines the total voltageof the stack, and the surface area of each of the cells determines thetotal current. The total electrical power generated by a given fuel cellstack can be determined by multiplying the total stack voltage by totalcurrent.

The term “electrode” is used herein to refer to the layers within thefuel cell MEA containing catalyst. The basic components that make thefuel cell electrodes include a catalyst, an electronic conductor, whichmay also support the catalyst, and an ionic conductor. In someimplementations, the electronic conductor comprises carbon which may ormay not be coated with a catalyst such as platinum, platinum alloy, oranother material. The ionic conductor may comprise an ion conductingpolymer. The ionic conductor facilitates conduction of ions through theelectrode layer. The electronic conductor facilitates conduction ofelectrons through the electrode layer. Electrodes generally contain acertain amount of void space (pores) for gas and/or liquid diffusioninto and out of the electrode layer.

Some embodiments described herein involve fuel cell electrodes thatinclude multiple ionic conductors, wherein the ionic conductors havedifferent characteristics. For example, each of the ionic conductors maycomprise an ionomer and at least one of the ionomers used in theelectrode layer may have one or more characteristics that differ fromthe characteristics of other ionomers in the electrode layer. As afurther example, the electrode layer may include two or more ionomersdiffering in type and/or equivalent weights (EWs) and/or form. As usedherein, “type” refers to characteristics of chemical structure and“form” refers to characteristics of physical shape and size, e.g.,different particle sizes or shapes.

The electrode layer has two major surfaces, a width, length, andthickness. In some implementations, the two or more ionomers in theelectrode layer may be distributed substantially uniformly between thetwo major surfaces throughout the thickness and/or length and/or widthof the electrode layer. In some implementations, the first ionomer mayhave a first distribution with in the electrode layer and the secondionomer may have a second distribution within the electrode layer. Forexample, one of the ionomers may be substantially uniformly distributedthrough the electrode layer and another of the ionomers may benon-uniformly distributed through the electrode layer.

In some embodiments, only one or at least one ionic conductor is used inthe electrode layer, and the distribution of the ionic conductor isnon-uniform within the electrode layer. The non-uniform distribution ofthe ionic conductor may provide networks rich in the ionic conductorwithin the electrode layer that enhance ionic conduction through theionic conductor rich networks. Complementary networks that arerelatively poor in the ionic conductor are also present in the electrodelayer and these complementary networks may be rich in the electronicconductor of the electrode layer. Thus, both ionic conductor richnetworks that enhance conduction of ions and electronic conductor richnetworks that enhance conduction of electrons may simultaneously existwhen at least one ionic conductor is non-uniformly distributed in theelectrode layer.

Embodiments described herein involve methods for the formation of fuelcell electrodes which include networks that enhance ionic conductionand/or electronic conduction through the electrode layer. The ionicand/or electronic conduction networks may traverse or partially traversethe thickness of the electrode layer. Fuel cell electrodes having ionicand electronic conduction networks may been formed in a fabricationprocess that uses an ionomer powder having particles with certainmorphological characteristics.

Fuel cell electrodes may be made from an “ink” formed by mixingcatalyst, electronic conductor, and an ionic conductor in solvent.According to some implementations, the ionic conductor used includessmall particles of an ion conducting polymer (denoted ionomer) suspendedand/or dissolved in solution, e.g., ionomer particles less than about 50nm in diameter. An ionic conductor with particles less than about 50 nmwhich are suspended and/or dissolved in solution is referred to hereinas “solution-based” ionic conductor. Ionomer particles in this sizerange may be formed by heating a solution of ionomer and water (or othersolvent) in a sealed enclosure to achieve high pressure at which pointthe ionomer dissolves into particles having diameters under about 50 nm.These small particles of ionomer may be mixed with a solvent, acatalyst, and an electronic conductor to form the electrode ink. Theelectrode ink is applied to a substrate and dried to form an electrodelayer as illustrated in FIG. 2A.

FIG. 2A is a diagram of a cross section of a typical electrode layer 200that is formed using a solution-based ionomer according to the processoutlined in the preceding paragraph. The electrode layer 200 is thin,having a thickness 291 which is small compared to the width 292 of theelectrode layer 200. FIG. 2B is a close up representation of a region210 (e.g., approximately a 2 micron×2 micron sized region) of theelectrode layer 200. The electrode structure illustrated in the close uprepresentation of the electrode layer region 210 results from mixing anionic conductor having small (<50 nm) particles in a solvent with acatalyst and an electronic conductor. The particles of the electronicconductor 220 (or catalyst coated electronic conductor) may havediameters of about 100 nm, for example. The catalyst may be coated onthe electronic conductor 220 or may otherwise be distributed within theelectrode layer, e.g., coated on catalyst support structures. FIG. 2Billustrates a cross section of the electronic conductor particles 220surrounded by the ionic conductor particles 230 forming ionic/electronicconductor structures 250. In this embodiment, the particles of the ionicconductor 230 and electronic conductor 220 are distributed substantiallyuniformly within the electrode layer 200.

Structure 250 in FIG. 2B may exist (as shown in FIG. 2C) as a smallparticles 230 dispersed on the surface of the electronic conductor (220)or as a coating (as shown in FIG. 2D) of ionomer 230 on the surface ofelectronic conductor 220. In all cases, the electronic conductor 220 mayor may not contain catalyst particles dispersed over its surface. FIGS.2B, 2C and 2D may be created using solution-based ionomer.

FIG. 2C is a depiction of an ionic/electronic conductor structure 250having an electronic conductor 220 which is substantially surrounded bynumerous small particles of the ionic conductor 230. In someembodiments, the electronic conductor 220 may be coated with a catalyst.

FIG. 2D illustrates a cross section of an ionic/electronic conductorstructure 250, in which the ionic conductor particles 230 are so smallin comparison to the electronic conductor 220 that the ionic conductorparticles form a film surrounding the electronic conductor 220. In thisexample, the electronic conductor 220 is coated with the catalyst 293.In some embodiments, the catalyst 293 may be disposed on supportstructures rather than the electronic conductor 220 and the catalystcoated support structures may be dispersed within the electrode layer200.

An electrode ink comprising an electronic conductor and a solution-basedionic conductor forms electrode layers having substantially uniformdistribution of ionic and electronic conductor materials through theelectrode layer as illustrated in FIG. 2B. Electrodes exhibitingsubstantially uniform distribution of ionic and electronic conductormaterials may not perform optimally during fuel cell operation due tothe incompatibility of various competing transport and conductionfunctions of the fuel cell electrode.

Some embodiments involve fuel cell electrodes that include non-uniformdistribution of only one or at least one ionic conductor and/or includemultiple ionic conductors which are uniformly or non-uniformlydistributed. In the embodiments using multiple ionic conductors, eachionic conductor is different in some characteristic from other ionicconductors in the electrode. These non-uniform and/or multiple ionicconductor implementations can provide enhanced durability and/orperformance when compared fuel cell electrodes having a single,uniformly distributed solution based ionic conductor. In implementationsthat use multiple ionic conductors, the multiple ionic conductors maycomprise different types of ionomers or may comprise the same type ofionomer having different forms. The fuel cell electrodes may alsoinclude multiple electronic conductors and/or multiple catalysts, whereeach electronic conductor or catalyst is different in somecharacteristic than the other electronic conductors or catalysts, suchas, e.g., equivalent weight.

FIGS. 2E and 2F provide an example of a multiple ionic conductorembodiment. FIG. 2E illustrates a cross section of a fuel cell electrodelayer 201 having a first major surface 214 and a second major surface215. The electrode layer 201 includes two ionic conductors 231, 241,e.g., two ionomers. In this example, a majority of the particles of thefirst ionomer 241 have diameters greater than about 1 μm. Ionicconductors that include particles, a majority of which have diametersgreater than solution based particles (e.g. greater than 50 nm orgreater than about 1 μm) are referred to herein as powdered ionicconductors. The second ionomer 231 is a solution based ionomer, whereina majority of the particles of the second ionomer 231 have diametersless than about 50 nm. In this embodiment, particles of the secondionomer 231 and the first ionomer 241 are intermixed with each other andwith the electronic conductor 221 throughout the electrode layer 201between the first major surface 214 and the second major surface 215.

FIG. 2F provides a close up representation of a region 211 of theelectrode layer (e.g., approximately a 2 micron×2 micron sized region)that depicts each of the first and second ionomers 241, 231, along withthe electronic conductor 221. In this implementation, particles of thesecond ionic conductor 231 coat the electronic conductor 221, as shownin cross section in FIG. 2F. Note that the electrode layer 201 alsoincludes a catalyst (not shown) which may be coated on the electronicconductor 221 and/or otherwise distributed throughout the electrodelayer 201, e.g., on catalyst support structures.

The larger diameter particles of the first ionomer 241 may be formed,for example, by cryogrinding, spray drying or other techniques. Althoughthe ionic and/or electronic conductor particles 221, 231, 241 arerepresented by spheres having smooth outer surfaces, the particles 221,231, 241 may have morphologies other than spheroid. For example, ionomerparticles formed by cryogrinding are not necessarily spheroid and mayhave rough surfaces (see, e.g., FIGS. 7A and 7B). Ionomer particlesformed by spray drying are spheroid with substantially smooth outersurfaces (see, e.g., FIG. 6). For example, substantially spherical(spheroid) particles with substantially smooth outer surfaces may havevariations in diameter less than about 10% and surface roughness lessthan about 5% of the diameter.

The use of two or more different ionomers may be beneficial to meet theconflicting requirements of a fuel cell electrode. For example, thesecond ionomer may provide superior catalyst support corrosionresistance and/or catalyst dissolution resistance characteristics to theelectrode layer when compared to the first ionomer, but provide reducedperformance when compared to the first ionomer. The use of these twotypes of ionomer mixed uniformly or non-uniformly within the electrodelayer may enhance both durability and performance. For example, thefirst ionomer may have a lower EW than the second ionomer. The firstionomer (lower EW ionomer) provides superior performance when the fuelcell is operating under hot/dry conditions. The second (higher EWionomer) provides superior performance when the fuel cell is operatingunder cold/wet conditions. The small particles of the second ionomer maycoat the electronic conductor to provide corrosion resistance andenhanced durability.

In some configurations, the ionomer particles may form agglomerations ofionomer particles which are distributed throughout the electrode layer.Without wishing to be bound by any particular theory, the affinity ofthe ionomer particles to form agglomerations may be related to themorphology of the ionomer particles. For example, it is believed thatthe approximately micron sized, substantially smooth, hollow, spheroidpowdered ionomer particles formed by spray drying are more likely toassociate in agglomerations.

FIG. 2G illustrates a cross section of electrode layer 202 that includesmicron sized powdered ionomer particles and does not include the smaller(<50 nm) solution-based ionomer particles. FIG. 2H provides a close uprepresentation of a region 212 of the electrode layer 202 (e.g.,approximately a 2 micron×2 micron sized region) that depicts micronsized powdered ionomer particles 242. Catalyst may be coated on theelectronic conductor particles 222 or may be otherwise distributedwithin the electrode layer 202.

In some embodiments, the electrode layer comprises multiple types orforms of powdered ionic conductor particles and each type or form of theionic conductor particles can be uniformly or non-uniformly distributedwithin the electrode layer. FIG. 2I illustrates a cross section ofelectrode layer 203 having a first major surface 214 and a second majorsurface 215. The electrode layer 203 includes particles of multiplepowdered ionic conductors 233, 243. In this embodiment, particles of thefirst ionic conductor 233 and particles of the second ionic conductor243 are intermixed with each other and with the electronic conductor 223throughout the electrode layer 203 between the first major surface 214and the second major surface 215. The electrode layer 203 may or may notinclude the smaller (<about 50 nm) solution-based ionomer particles.

FIG. 2J provides a close up representation of a region 213 of theelectrode layer 203 (e.g., approximately a 2 micron×2 micron sizedregion) that includes first powdered ionomer particles 233 and secondpowdered ionomer particles 243. For example, the multiple powdered ionicconductors 233, 243 may comprise different types of powdered ionomers.As another example, the multiple powdered ionic conductors may comprisethe same type of powdered ionomer, but may be different forms of thesame type of powdered ionomer, e.g., one form could be spray driedionomer and the other form could be cryoground ionomer. Catalyst may becoated on the electronic conductor particles 223 and/or may be otherwisedistributed within the electrode layer 203.

Some embodiments involve fuel cell electrodes that include regionalionic and/or electronic conductor-rich networks that at least partiallytraverse the thickness of the electrode layer. The ionic conductor andelectronic conductor materials in these electrodes are non-uniformlydistributed so that regions within the electrode layer have relativelymore ionic conductor material, e.g., as measured by weight or volume,than electronic conductor material and/or regions within the electrodelayer have relatively more electronic conductor material, e.g., asmeasured by weight or volume, than ionic conductor material. FIG. 3A isa diagram of a cross section of an electrode layer 300 comprisingpowdered ionic conductor particles that form ionic conductor richnetworks. The electrode layer 300 has a thickness 291 which is smallcompared to the width 292 of the electrode layer. FIG. 3B provides aclose up representation of a region 310 of the electrode layer 300(e.g., approximately a 2 micron×2 micron sized region). The electrodestructure illustrated in FIGS. 3A and 3B can be formed from an electrodeink which is a mixture of a powdered ionic conductor with powderparticles greater than about 1 μm, a catalyst, an electronic conductor,and a solvent.

FIG. 3B illustrates the ionic conductor material 330 and the electronicconductor material 320 distributed in a plurality of ionic conductorrich networks 340 and a plurality of electronic conductor rich networks350. The ionic conductor rich networks 340 (also referred to herein as“ionic conductor networks”) have a volume ratio of ionic conductor toelectronic conductor that is greater than the volume ratio of ionicconductor to electronic conductor within the electronic conductor richnetworks 350 (also referred to herein as “electronic conductornetworks.” The electronic conductor networks 350 have a volume ratio ofelectronic conductor to ionic conductor that is greater than the volumeratio of electronic conductor to ionic conductor within the ionicconductor networks 340. The electronic conductor networks 350 aresubstantially discrete and separate from the ionic conductor networks340. The affinity for some types of ionomer particles (micron sizedparticles that are smooth, spheroid and/or hollow) to form particleagglomerations may contribute to the formation of the ionic conductornetworks 340 and/or the electronic conductor networks 350. The ionicconductor networks 340 provide lower resistance paths 341 for ionconduction when compared with the electronic conductor networks 350. Theelectronic conductor networks 350 provide lower resistance paths 351 forelectron conduction when compared with the ionic conductor networks 340.When ionic conduction and electronic conduction networks are present inthe electrode layer, conduction of electrons can occur predominantlywithin the electronic conductor rich networks and conduction of ions canoccur predominantly within the ionic conductor rich networks when thefuel cell is in operation.

Fuel cell electrodes with ionic and electronic conductor networks, asshown in FIGS. 3A and 3B, may exhibit superior performance when comparedto the electrode layers which have ionic and/or electronic conductormaterials that are substantially uniformly distributed through theelectrode layer. For example, the superior performance characteristicsof the networked electrodes may include superior material transportand/or superior electrical conduction properties. The electrodes havingionic and/or electronic conductor networks may also exhibit superiordurability properties when subjected to the ranges of temperature,electrical potential, and relative humidity encountered during fuel celloperation.

Without wishing to be bound by any particular theory, the formation ofthe substantially discrete ionic and/or electronic conductor networkscould be related to the phase of the ionic conductor material when it ismixed with the electronic conductor material during fabrication of theelectrode layer. For example, mixing the ionic conductor which comprisessmall size particles (<about 50 nm particles suspended or dissolvedsolution) with the electronic conductor appears to create an electrodelayer that exhibits a more uniform distribution of the ionic andelectronic conductors as in the electrode layer illustrated in FIGS. 2Aand 2B. In contrast, mixing certain types or forms of ionic conductorwith the electronic conductor material produces an electrode layerexhibiting ionic and electronic conductor networks as illustrated inFIGS. 3A and 3B. Again, without wishing to be bound by any particulartheory, ionomer particles that are micron sized spheroid, relativelysmooth, and/or hollow appear to more readily form the networks thatprovide enhanced ionic and electronic conduction pathways.

In some implementations, multiple types of ionomer may be used to formthe electrode layer, with at least a first type of ionomer contributingto ionic conductor networks in the electrode layer. The second ionomermay or may not contribute to the ionic conductor networks. The secondionomer may be distributed substantially uniformly or non-uniformly inthe electrode layer.

FIG. 3C is a cross section illustrating an electrode layer 301comprising an electronic conductor 380, e.g., catalyst coated carbon,and first and second ionomers 375, 370. The electrode layer 301 includesa first major surface 312 and a second major surface 313. FIG. 3Dprovides a close up representation of a portion 311 of the electrodelayer 301 (e.g., approximately a 2 micron×2 micron sized region). Theelectrode structure illustrated in FIG. 3D can be formed from anelectrode ink which is a mixture of a first ionic conductor 375comprising powdered particles greater than about 1 μm, a second ionicconductor 370 comprising particles less than about 50 nm, a catalyst, anelectronic conductor 380, and a solvent. In this embodiment, particlesof the first ionic conductor 375 and particles of the second ionicconductor 370 are intermixed with each other and with the electronicconductor 380 throughout the electrode layer 301 between the first majorsurface 312 and the second major surface 313. In some implementations,the amount of the first ionic conductor 375 in the electrode layer isgreater than the amount of the second ion conductor 370 by volume. Forexample, the first ionic conductor 375 may comprise a spray dried and/orcryoground powdered ionomer and the second ionic conductor 370 maycomprise the solution based ionomer as previously discussed.

The close up representation 311 illustrates the first ionic conductormaterial 375 and the electronic conductor material 380 distributed in aplurality of ionic conductor rich networks 340 and a plurality ofelectronic conductor rich networks 350. The second ionic conductormaterial 370 may surround and/or coat the electronic conductor particles380 as depicted in FIG. 3D and/or may be distributed relativelyuniformly through the electrode layer. The first ionic conductor 375 maycomprise larger particles than the second ionic conductor, and may formionic conductor networks 340 which facilitate transport of ions andwater through the electrode layer 301. Formation of the ionic conductornetworks 340 may be promoted because the powdered ionomer 375 has anaffinity for agglomeration when the electrode layer is being formed, andthese agglomerations form at least portions of the ionic conductornetworks 340.

The ionic conductor networks 340 have a volume ratio of ionic conductorto electronic conductor that is greater than the volume ratio of ionicconductor to electronic conductor within the electronic conductor richnetworks 350. The electronic conductor networks 350 have a volume ratioof electronic conductor to ionic conductor that is greater than thevolume ratio of electronic conductor to ionic conductor within the ionicconductor networks 340. The ionic conductor networks 340 provide lowerresistance paths 341 for ion conduction when compared with theelectronic conductor networks 350. The electronic conductor networks 350provide lower resistance paths 351 for electron conduction when comparedwith the ionic conductor networks 340.

The electrode layer structure illustrated in FIG. 3D may provideenhanced durability and/or performance. For example, the second ionomer370 may provide superior catalyst support corrosion resistance and/orcatalyst dissolution resistance characteristics to the electrode layer301 when compared to the first ionomer 375, and the first ionomer 375may provide enhanced performance characteristics to the electrode layer301 when compared to the second ionomer 370. In some implementations,the second ionomer 370 may have a higher EW than the first ionomer. Thesecond ionomer (higher EW ionomer) may provide superior characteristicsthan the first ionomer 375 when the fuel cell is operating under hot/dryconditions. The first ionomer 375 (lower EW ionomer) may providesuperior characteristics than the second ionomer 370 when the fuel cellis operating under cold/wet conditions.

Processes for forming electrode layers involve forming an ink comprisinga catalyst, an electronic conductor, an ionic conductor, and a solvent.More than one type and/or form of catalyst, electronic conductor, ionicconductor, and/or solvent may be used. For example, the ionic conductormay comprise perfluorinated sulfonic acid (PFSA), and/or perfluorinatedimide acid (PFIA), and/or a hydrocarbon. PFIA is described in commonlyowned U.S. Patent Application No. 61/325,062, filed Apr. 16, 2010,Hamrock et al. which is incorporated herein by reference. The solventmay comprise water, an alcohol, and/or a hydrocarbon, for example. Thecatalyst may comprise platinum, palladium, bimetals, metallic alloys,and/or carbon nanotubes. The catalyst may be coated on the electronicconductor, e.g., the electronic conductor and catalyst may compriseplatinum coated carbon. In some embodiments, the catalyst may be coatedon support elements other than the electronic conductor, such as thenanostructured supports described in U.S. Pat. No. 5,879,827. Theelectronic conductor may have particles with diameters of about 100 nm,for example, and may comprise carbon, tin oxide, and/or titanium oxide,and/or other suitable materials.

Specific amounts of each component of the electrode ink may be varied toachieve a desired viscosity, e.g., about 1000 centipoise, and solidscontent, e.g., about 2% to about 40% solids by weight. The electrode inkmay be prepared by adding the ink components and then mixing the inkcomponents for a period of time. In some implementations, the mixing mayinclude adding media, such as 6 mm diameter ceramic beads and thenrolling or ball milling for at least about 5 minutes. The prepared inkis then applied to a substrate, such as a major surface of a fuel cellelectrolyte membrane, a GDL, or a liner, and dried. The dried ink layerforms the fuel cell electrode.

FIGS. 4A and 4B illustrate exemplary processes for forming a fuel cellelectrode. As depicted in the flow diagram of FIG. 4A, an electrode inkmay be formed by combining 410 the electronic conductor, catalyst, ionicconductor, and solvent and mixing 420 these ingredients for a period oftime. For example, the electronic conductor, catalyst, ionic conductor,and solvent may be combined, e.g., combined substantiallycontemporaneously, and then mixed. After mixing, the ink is coated 430on a substrate and allowed to dry 440 to form the fuel cell electrodelayer. The ionic conductor of the electrode ink may comprise only onetype of ionic conductor, e.g., an ionomer in the form of particles, amajority of which have diameters greater than about 50 nm or greaterthan about 1 μm. These ionomer particles may have substantially smooth,spheroid, and/or hollow morphology which can be produced by a spraydrying process. As previously discussed, ionomer particles of this sizeand morphology may more readily form electrode layer structures thatinclude ionic conductor networks.

Multiple types of ionomer and/or multiple forms of the same ionomer maybe included in the ionic conductor forming the electrode ink. Whenmultiple forms of the same ionomer are used, the multiple forms may bemultiple different particle sizes and/or the multiple types may bemultiple different EWs of what is otherwise the same type of ionomer.For example, a first ionomer of the multiple ionomers may be powdered,with a majority of particles having diameters greater than about 1 μm,for example. A second ionomer of the multiple ionomers may be solutionbased, with a majority of particle diameters less than about 50 nm. Thefirst and second ionomers may be the same type of ionomer or may bedifferent types of ionomers.

FIG. 4B illustrates another exemplary process for forming a fuel cellelectrode. According to this process, an electrode ink pre-mixture isformed 450 by combining the catalyst, electronic conductor and solvent.The pre-mixture ingredients are mixed 452, e.g., by ball milling, for aperiod of time, such as about 24 hours. After mixing the pre-mixtureingredients, a first ionic conductor, e.g., powdered ionomer particlescomprising substantially smooth surfaced, hollow, spherical particles, amajority of which have diameters greater than 50 nm or greater thanabout 1 μm are added 454 to the pre-mixture. A second ionomer, e.g.,having a majority of particles with diameters less than about 50 nm, maybe used to form the pre-mixture, and/or may be added along with thefirst ionomer and/or may be added later in the process. After the firstionomer is added 454, the ink is mixed 456 for an additional time, e.g.,about 30 minutes. Additional powdered or solution based ionic conductorsmaybe added to the pre mixture and/or at a later stage in the process.The electrode ink is coated 458 on a substrate and dried 460. In someimplementations, forming the ink may involve adding a first portion ofan ionic conductor along with the catalyst, electronic conductor, andsolvent, mixing, and then adding a second portion of the ionic conductorand mixing. Mixing can be accomplished by a variety of processes,including ball milling, stirring, shearing, sonication, etc.

The electrode structure resulting from the processes described inconnection with FIG. 4A or 4B may be used to form electrode layershaving multiple ionomers and/or may be used to form electrode layershaving discrete networks rich in an ionic conductor which aresubstantially separate and discrete from networks rich in an electronicconductor material. FIG. 5A is an optical image of the surface of a fuelcell electrode formed using a solution based ionic conductor comprisingsmall particles, a majority of which have diameters less than about 50nm. FIG. 5B is an optical image of the surface of a fuel cell electrodelayer formed using a powdered ionomer which comprises larger particles,a majority of which have diameters greater than about 1 μm, and havingsubstantially smooth, spheroid, hollow morphology. The optical image ofFIG. 5B shows the larger ionomer particles which may form ionomer richzones 510.

As previously discussed, when multiple ionomers are used, severaldifferent types of ionomers, or the same type of ionomer in severaldifferent forms may be used. At least one of the ionomers differs fromthe other ionomers in at least one characteristic. For example, usingdifferent types or forms of the ionomer may involve using different EWof what is otherwise the same type of ionomer and/or using the sameionomer having different particles sizes and/or different size rangesand/or different particle morphologies. For example, using multipledifferent types of ionomer may involve using PFIA as one of the multipletypes of ionomer and using PFSA as another of the multiple types ofionomer. If different types of ionomer are used, each of the ionomersmay have the same form, or each ionomer may a different form (e.g., oneionomer having small particles and the other ionomer having largerparticles), and/or the multiple ionomers may comprise different EWmaterials. The same amount, measured for example, by volume or weight,of each ionomer or a different amount of each ionomer may be used in theelectrode ink.

When forming the electrode, the different types or forms of ionomer maybe added simultaneously or sequentially to the mixture. For example,sequentially adding the ionomers may involve forming an electrode inkusing a first ionomer (e.g., according to the process described inconnection with FIG. 4), grinding the electrode ink, and then mixing theground electrode ink with a solvent and a second ionomer.

Spray drying is a useful method for forming a powdered ionomer that canbe used to make fuel cell electrodes that include ionic conductornetworks that are substantially discrete and separate from electronicconductor networks as depicted, for example, in FIG. 3B. As discussed inmore detail in the examples below, powdered ionomer formed by spraydrying has been shown to produce superior fuel cell electrodes whencompared to powdered ionomer that is produced by other methods. Morespecifically, fuel cell electrodes fabricated using ionomer powderproduced by spray drying have shown superior performance with comparedto fuel cell electrodes fabricated using ionomer powder produced bycryogrinding, for example. The difference in performance between theelectrodes formed using the spray dried ionomer powder and electrodesformed using other types of ionomer powder may be related to themorphology of the powder particles.

As illustrated in the scanning electron microscope (SEMS) image of FIG.6, spray drying ionomer can produce powder particles that are spheroids,having outer surfaces that are substantially smooth and which arehollow. The term spheroid is used to describe a particle having adiameter that does not vary more than about 10%. The term “substantiallysmooth” is used to describe particles having surface roughness less thatabout 5% of the diameter of the particle.

The powdered ionomer particles produced by spray drying, for example,may range in size from about 50 nm to about 30 μm or may range from 50nm to about 15 μm, or may range from about 1 μm to about 15 μm. Theaverage diameter of the particles may be about 3.5 μm. The average sizeof the spray dried particles can be controlled within a range of lessthan 1 micron to greater than a 1 millimeter by changing the variablesof the spray drying process, including spray velocity, solutionconcentration, and chamber temperature, for example. The diameter rangecan also be controlled by varying these processing parameters. Amajority of the spray dried ionomer spheroids may be hollow. In someimplementations, an additive, such as cerium and/or manganese compounds,may be used during the spray drying process and/or at other stagesduring formation of the electrode ink.

For example, spray drying to achieve ionomer particles having thecharacteristics described above may involve taking a dispersion offluorinated polymer and water, atomizing the dispersion into smalldroplets of dispersion, then releasing the dispersion droplets into aheated gas (air) which dries the dispersion to produce flowableparticles of polymer. These particles have a dry exterior surface but aninternal residual moisture level of about 2% to 10%. The processvariables for spray drying include: 1) % solids of the input dispersion,2) atomization pressure of the feed, 3) feed rate, 4) inlet temperatureof the heated gas (e.g., air), and 5) outlet temperature of the cooledgas. These variables affect the residual moisture level and/or thedistribution of the measured particle size of the polymer powder.Exemplary ranges for the spray drying process variables that can produceionomer particles as described herein include: 1) percent solids ofdispersion in a range of about 9% to about 22%, or a range of about 18%to about 20%, 2) atomization pressure in a range from about 30 psi toabout 60 psi, or a range of about 35 psi to about 40 psi, 3) feed rate(as measured by pump speed) in a range of about 50 rpm to about 140 rpmand adjusted based on % solids and outlet temperature, 4) inlettemperature in a range of about 160° C. to about 250° C., or about 185to about 200° C., 5) outlet temperature in a range of about 65° C. toabout 95° C., or about 85° C. to about 90° C.

Cryogrinding is another process that produces a powdered ionomer.However, in contrast to the smooth, hollow, spheroid ionomer particlesshown in the SEMS image of FIG. 6, cryogrinding produces irregularparticles with jagged surfaces, as illustrated in SEMS images FIGS. 7Aand 7B. The size of the cryoground particles varies from very smalldust-like particles of less than 1 micron to particles that exceed 20microns.

The differences in the ionomer particle morphology, e.g., such asbetween particles formed by spray drying and particles formed bycryogrinding, may influence ink rheology and/or fuel cell electrode porestructure, and/or fuel cell electrode performance. The spheroid,substantially smooth, and hollow ionomer particles formed by spraydrying appear to facilitate the formation of the discrete ionicconductor rich and electronic conductor rich networks within the fuelcell electrode.

Fuel cell electrodes must be capable of performing multiple functionsover a wide range of operating conditions. The functions performed bythe fuel cell electrodes include gas diffusion of fuel or oxidant,transport of liquid water, and electronic and ionic conduction throughthe electrode layer. Fuel cell electrodes need to perform thesefunctions over a wide range of conditions from about −40 C to greaterthan about 10° C., with reactant gas humidity ranging from 0 to 100%.

The fuel cell electrode is required to efficiently and simultaneouslyperform multiple material transport and electrical conduction functionswhen the fuel cell is operating. These material transport and electricalconduction functions include diffusion of fuel gases or oxidant gases,transport of liquid water, and conduction of protons and electronswithin the electrode layer. All of these functions may not besimultaneously and optimally accommodated in some fuel cell electrodesthat have a substantially uniform distribution of a single type of ionicconductor. The ability with which the electrode layer can transportliquid water is of particular interest with respect to the cathodeelectrode where water is formed. Within the porous layers of a fuel cellelectrode, for example, enough pores must be sufficiently hydrophobic toprevent liquid water from filling too much of the layer. Overfilling ofthe layers or regions within the layer with liquid water is typicallyknown as “flooding”. The flooding of pores prevents reactant gases frompenetrating the electrode and reaching catalyst sites, resulting inperformance loss.

An overly hydrophobic layer is also not ideal for fuel cell operation.At cool temperatures, water must migrate from the electrodes to the flowfield as a liquid. If the layer through which the water migrates is toohydrophobic, there are no liquid connections through which water canreadily move. The water must percolate from pore to pore, a processwhich requires significant build up of liquid pressure. This high liquidpressure results in flooding of pores, reduction of gas transport andloss of fuel cell performance. Appropriate engineering of hydrophilicand hydrophobic pores can provide both liquid water and gas transportsimultaneously.

Substantially uniform distribution of small diameter ionic conductorparticles within a fuel cell electrode may produce small pore sizeswithin the electrode layer, resulting in compromised liquid transportand/or gas diffusion. Poor ionic and/or electronic conduction may occurdue to narrow pathways through the well mixed, small particle sizeionomer, electronic conductor, and catalyst. Substantially uniformdistribution of the ionomer may result in reduced pathways for liquidtransport due to the slightly hydrophilic properties of the ionomer.Water transport may be poor due to limitations on the maximum amount ofionomer allowed in an electrode before flooding. Electron conduction maybe reduced due to poor carbon-carbon contact.

For optimal performance, the fuel cell electrodes need to provide aporous layer that readily conducts gases to reaction sites within theelectrodes and also transports liquid water away from the reactionsites. The electrode layer should have sufficient hydrophilicity toallow easy liquid water transport yet sufficient hydrophobicity toprevent flooding of the pores by the liquid water. Regions of excessivehydrophobicity may create a “wall” with the electrode that requires highliquid pressure for the liquid water to break through the wall. Abuildup of liquid pressure behind the wall may create flooding of otherregions, which prevents fuel gases from reaching the reaction sites. Ifthe fuel cell electrode includes hydrophilic regions of sufficientnumber and size, flooding can be prevented.

Fuel cell electrodes must include a sufficient amount of ionic conductorto allow rapid ion conduction to the reaction sites (in the cathodeelectrode) and to allow rapid ion conduction away from the reactionsites (in the anode electrode). However the fuel cell electrode mustalso include a sufficient amount of electronic conductor to allow rapidelectron conduction to the reaction sites (in the cathode electrode) andrapid electron conduction away from the reaction sites (in the anodeelectrode).

Fuel cell electrodes having discrete ionic and/or electronic conductornetworks can provide superior liquid and gas transport, hydrophobicity,hydrophilicity, and electron an ion conduction when compared with fuelcell electrodes having substantially uniformly distributed ionic andelectronic conductor materials.

The use of ionomer particles that are generally greater than about 1 μmin diameter in the fuel cell ink appears to facilitate the formation ofionic and electronic conductor networks. Furthermore, the morphology ofparticles used in the fuel cell ink may also be a factor, with thesubstantially smooth and hollow spheroid particles produced by the spraydrying process providing superior characteristics when compared to thejagged, irregular particles produced by cryogrinding. The narrower sizerange of the spray dried powder particles (in contrast with the widersize range of the cyroground powder particles) may also contribute toenhanced electrode performance.

The smooth, hollow spheroids produced by spray drying appear to promoteagglomerations of the ionomer powder particles and creation of ionicconductor rich networks (which are relatively electronic conductorpoor). For example, when catalyst coated carbon is used as the catalystand electronic conductor, the electronic conductor rich regions containnon-oxidized carbon (natural C) which is hydrophobic. The carbon richregions that ideally substantially traverse the electrode layer providepathways that facilitate electronic conduction and also provide networksof low liquid water content, thus allowing fast gas transport. The ionicconductor rich regions are moderately hydrophilic. Uniform distributionof the ionic conductor is subject to the formation of pockets offlooding. However ionic conductor rich networks that substantiallytraverse across the electrode layer provide pathways for rapid protonand water conduction.

As previously discussed, the ionic conductor networks and electronicconductor networks can provide complementary functions with the fuelcell electrode. When these complementary networks are present in theelectrode layer, the conflicting performance constraints of optimalelectrode design (fuel and oxidant gas transport, liquid watertransport, and electron and proton conduction) can be betteraccommodated. The presence of the electronic and ionic conductornetworks serve to maintain fuel cell performance by facilitatingtransport of gases to and from the reaction sites and conduction of ionsand electrons to and from the reaction sites of the electrode layer. Theionic conductor and electronic conductor networks can provide anextended operating range for the fuel cell. For example, because liquidwater transport is improved along the ionic conductor networks, a lowerEW ionomer may be used as the ionic conductor. The lower EW materialachieves better performance in hotter, drier conditions, whilepreventing flooding at colder, wetter conditions. Alternatively, theaddition of a higher EW ionomer may be used to increase the durabilityof the electrode layer.

Objects and advantages of this disclosure are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this disclosure.

EXAMPLES

MEAs having four different types of fuel cell cathode electrodes wereconstructed and tested. The MEAs were produced by the same process,using identical materials, except for the cathode electrode. Thedifferent cathode electrode types were formed from 1) electrodes formedusing a solution-based ionomer (SOLN, SOLN 2) having relatively smallsize particles (e.g., diameters less than 50 nm) in solution, 2)electrodes formed using a spray dried ionomer powder (PDR, PDR 2), (seeFIG. 6 and associated discussion), 3) electrodes formed by pre-mixingthe catalyst/electronic conductor prior to combining the spray driedionomer powder (PDR postBM), and 4) electrodes formed using a cryogroundpowder (cryoPDR) (see FIGS. 7A and 7B and associated discussion). Thefabrication parameters of the test MEAs are provided in Table 1. TheSOLN electrodes formed using the solution based ionomer were fabricatedby the process outlined in the flowchart of FIG. 4A. The PDR electrodesformed using the spray dried ionomer powder were fabricated by theprocess outlined in FIG. 4A. The PDR post BM electrode was fabricated byprocess outlined in FIG. 4B. The electrode formed using the cryo groundionomer powder was fabricated by process outlined in FIG. 4A.

TABLE 1 MEA with MEA with MEA with spray MEA with cryoground spray drieddried powdered solution-based powdered powdered ionomer ionomer ionomerionomer electrode post electrode electrode electrode ball milled (PDR(SOLN) (cryoPDR) (PDR) post BM) Cathode design variablesIonomer/Catalyst 0.8 0.8 0.8 0.8 weight ratio Ionomer 3M800EW 3M800EW3M800EW 3M800EW (available from 3M Company, St. Paul, MN, USA) Form ofionomer Aqueous Cryoground Spray dried Spray dried used for solutionpowder powder powder electrode Catalyst TKK 10V30E TKK 10V30E TKK 10V30ETKK 10V30E (available from Tanaka Kikinzoku Kogyo (TKK), Tokyo, Japan)Ink mixing Ball milling Ball milling Ball milling 2 step ball techniqueafter combining after after milling process all components combining allcombining all ionomer added components components after ball millingcatalyst and solvent Solvent Aqueous Aqueous Aqueous Aqueous Ink solids20% 20% 20% 20% content Catalyst loading 0.3 0.3 0.3 0.3 (mg Pt/cm2)Electrode Hand painting Hand painting Hand painting Hand paintingcoating method Annealing 150 C, 30 min. 150 C, 30 min. 150 C, 30 min.150 C, 30 min. Anode design variables Ionomer/Catalyst 0.8 0.8 0.8 0.8ratio Ionomer 3M1000EW 3M1000EW 3M1000EW 3M1000EW (available from 3MCompany, St. Paul, MN, USA) Form of ionomer Aqueous Aqueous AqueousAqueous used for solution-based solution-based solution-basedsolution-based electrode ionomer ionomer ionomer ionomer Catalyst TKK10V30E TKK 10V30E TKK 10V30E TKK 10V30E Ink mixing Ball milling Ballmilling Ball milling Ball milling technique Solvent Aqueous AqueousAqueous Aqueous Ink solids 20% 20% 20% 20% content Catalyst loading 0.10.1 0.1 0.1 (mg Pt/cm2) Electrode Hand painting Hand painting Handpainting Hand painting coating method Annealing 150 C, 30 min. 150 C, 30min. 150 C, 30 min. 150 C, 30 min. Anode Design Variables GDL typeHydrophobized Hydrophobized Hydrophobized Hydrophobized carbon papercarbon paper carbon paper carbon paper with with with with microporousmicroporous microporous microporous layer layer layer layer MembraneDesign Variables Membrane 3M800EW 3M800EW 3M800EW 3M800EW materialThickness 0.8 mil 0.8 mil 0.8 mil 0.8 mil

In one analysis, the MEAs with the spray dried powdered ionomerelectrodes (denoted PDR) were compared to the MEAs having solution basedionomer electrodes (denoted SOLN). Three MEAs were made using the spraydried powdered ionomer and three MEAs were constructed using thesolution based ionomer for each trial. Two trials of each of the threeMEAs constructed were completed for each group. The results of the firsttrial of the spray dried powdered ionomer electrode group are denotedPDR; the results of the second trial of the spray dried powdered ionomerelectrode group are denoted PDR 2; the results of the first trial of thesolution based ionomer electrode group are denoted SOLN; the results ofthe second trial of the solution based ionomer electrode group aredenoted SOLN 2.

Catalytic activity: Catalyst activity was measured and is shown for MEAswith the spray dried powder ionomer electrodes and the solution basedionomer electrodes in Table 2. The catalyst activity of the powder basedelectrodes shows improvement when compared with the catalyst activity ofthe solution based electrodes. These activity gains may be explained bybetter three phase interface (catalyst, ionomer, and reactant gas)created by the powder based ionomer electrodes.

TABLE 2 Catalyst Loading SEF Activity Fuel cell Type mg/cm2 (cm2/cm2)(m2/g) 1 solution 0.283 129 45.58 2 solution 0.315 139 44.12 3 solution0.298 126 42.28 4 spray dried 0.294 156 53.06 powder 5 spray dried 0.291153 52.58 powder 6 spray dried 0.295 154 52.20 powder

Galvano-dynamic polarization scanning (GDS) analysis: FIG. 8 shows theGDS polarization performance results for two trials of the MEAs withsolution-based ionomer electrodes (SOLN. SOLN 2) and the powder-basedionomer electrodes (PDR, PDR 2). The test conditions were as follows:cell temperature=70 C, anode and cathode inlet humidification=100%,ambient operating pressure, fuel (H2) stoichiometric ratio=1.4, oxidant(air) stoichiometric ratio=2.5. For a given current density, thepowder-based ionomer electrodes show higher voltages than thesolution-based ionomer electrodes. This benefit is more significant athigh current densities.

FIG. 9 compares the MEA performance of the SOLN and PDR electrodes at acurrent density of 1.2 A/cm2 and 1.5 A/cm2. The data illustrated in FIG.9 indicates that higher cell voltages are achieved by the spray driedpowdered ionomer electrodes (PDR, PDR 2) than the solution-basedelectrodes (SOLN, SOLN 2) at higher current densities. Note that data at1.5 A/cm2 was only recorded for the second trial of electrodes (SOLN 2,PDR 2).

A follow up analysis was performed to compare various properties ofspray dried powdered ionomer electrodes formed by adding ink componentstogether and mixing (denoted PDR), spray dried powdered ionomerelectrodes formed by pre-mixing Pt coated carbon and solvent (water)prior to adding the spray dried powdered ionomer (denoted PDR post BM),cryoground powdered ionomer electrodes (denoted cryoPDR), and solutionbased ionomer electrodes (denoted SOLN).

Electrochemical Surface Area: The electrochemical surface area (ECSA) ofthe catalyst was analyzed for each of the electrode types PDR, PDR postBM, cryoPDR, SOLN listed in the preceding paragraph. The ECSA analysisprovides the catalyst surface that is available to contribute to thefuel cell reaction. A larger ECSA is associated with better fuel cellperformance. The ECSA was performed for electrodes under the followingtest conditions: 40 C cell temperature, 70 C dew point (anode andcathode); H2/N2 (anode/cathode), flow rate 800/500 SCCM anode/cathode.The ECSA readings were taken at 50 mV/s scan rate from 0.05 to 0.80 V.The graph of FIG. 10 provides a comparison of the electrochemicalsurface area of the electrode types listed above. As can be appreciatedfrom FIG. 10, the cryoground powdered ionomer (cryoPDR) electrodes showthe highest ECSA at 70 m2/g Pt. Both the PDR electrodes and the PDR postBM electrodes also show ECSA improvements over the solution based (SOLN)ionomer electrodes.

Catalytic Activity: The catalytic activity at 0.9 V was measured foreach MEA under the following conditions: T=80 C, 100% RH, H2/O2(anode/cathode), 7.5/7.5 psig pressure (anode cathode). The catalyticactivity measurements for the MEAs are provided in FIG. 11. The cryoground powdered ionomer electrode performed better than the solutionbased ionomer electrode in this test. The spray dried powdered ionomerelectrodes (PDR and PDR post BM) exhibited more catalytic activity onaverage per unit mass than the cryo ground powdered ionomer electrodesand the solution based ionomer electrodes.

Follow-up galvano-dynamic polarization scanning (GDS): Galvano-dynamicpolarization scanning was performed for MEAs having SOLN, PDR, cryoPDRand PDR post BM electrodes. The test conditions were as follows: celltemperature=70 C, anode and cathode inlet humidification=100%, ambientoperating pressure, fuel (H2) stoichiometric ratio=1.7, oxidant (air)stoichiometric ratio=2.5. FIG. 12 shows the GDS polarization curve forthe SOLN, PDR, cryoPDR and PDR post BM MEAs. FIG. 13 provides the MEAperformance at a current density of 1.2 A/cm2 for each type ofelectrode. In this analysis, all of the powder based electrodesoutperformed the solution based electrodes. The PDR and PDR post BM showthe greatest improvement over the solution based electrodes and wereexhibited improved high current density over that of the cryoPDRelectrodes.

Objects and advantages of this disclosure are further illustrated by thefollowing listing of representative embodiments, but the particularmaterials, amounts, conditions and details, recited in these embodimentsshould not be construed to unduly limit this disclosure.

EMBODIMENTS

Embodiment 1 is a fuel cell subassembly, comprising:

an electrode layer, comprising:

-   -   a catalyst;    -   an electronic conductor;    -   an ionic conductor;    -   a plurality of electronic conductor rich networks within the        electrode layer; and    -   a plurality of ionic conductor rich networks within the        electrode layer and interspersed with the electronic conductor        rich networks, wherein a volume ratio of the ionic conductor to        the electronic conductor is greater in the ionic conductor rich        networks than in the electronic conductor rich networks.        Embodiment 2 is the fuel cell subassembly of embodiment 1,        wherein, during operation of a fuel cell that includes the fuel        cell subassembly, conduction of electrons occurs predominantly        within the electronic conductor rich networks and conduction of        ions occurs predominantly within the ionic conductor rich        networks.        Embodiment 3 is the fuel cell subassembly of embodiment 1,        wherein the ionic conductor comprises particles of a spray dried        ion conducting polymer.        Embodiment 4 is the fuel cell subassembly of embodiment 1,        wherein the ionic conductor comprises particles and a majority        of the particles have an outer surface that is substantially        smooth.        Embodiment 5 is the fuel cell subassembly of embodiment 1,        wherein the ionic conductor comprises particles and a majority        of the particles are spheroids having a variation in diameter of        less than about 10%.        Embodiment 6 the fuel cell subassembly of embodiment 1, wherein        the ionic conductor comprises particles and a majority of the        particles are hollow.        Embodiment 7 is the fuel cell subassembly of embodiment 1,        wherein the ionic conductor comprises particles and a majority        of the particles have diameters in a range of about 1 μm to        about 15 μm.        Embodiment 8 is the fuel cell subassembly of embodiment 1,        wherein the electronic conductor comprises electronic conductor        particles and the catalyst is disposed on the electronic        conductor particles.        Embodiment 9 is the fuel cell subassembly of embodiment 1,        wherein the catalyst is disposed on nanostructured supports.        Embodiment 10 is the fuel cell subassembly of embodiment 1,        wherein the electronic conductor comprises one or more of        carbon, tin oxide, and titanium oxide.        Embodiment 11 is the fuel cell subassembly of embodiment 1,        wherein the catalyst comprises one or more of platinum,        palladium, bimetals, metallic alloys, and carbon nanotubes.        Embodiment 12 is the fuel cell subassembly of embodiment 1,        wherein the ionic conductor comprises a first ion conducting        polymer and the electrode layer further comprises a second ionic        conductor comprising a second ion conducting polymer.        Embodiment 13 is the fuel cell subassembly of embodiment 12,        wherein the first ion conducting polymer has a first equivalent        weight and the second ion conducting polymer has a second        equivalent weight.        Embodiment 14 is the fuel cell subassembly of embodiment 12,        wherein:    -   the first ion conducting polymer comprises particles, and a        majority of the particles of the first ion conducting polymer        have diameters greater than about 1 μm; and    -   the second ion conducting polymer comprises particles, and a        majority of the particles of the second ion conducting polymer        have diameters less than about 50 nm.        Embodiment 15 is the fuel cell subassembly of embodiment 14,        wherein the particles of the second ion conducting polymer form        a film on the electronic conductor and the particles of the        first ion conducting polymer comprise a majority of the volume        of the ionic conductor.        Embodiment 16 is the fuel cell subassembly of embodiment 14,        wherein the first ion conducting polymer substantially forms the        ion conducting networks.        Embodiment 17 is the fuel cell subassembly of embodiment 1,        wherein the electrode layer is disposed on an electrolyte        membrane.        Embodiment 18 is the fuel cell subassembly of embodiment 1,        wherein the electrode layer is disposed on a gas diffusion        layer.        Embodiment 19 is the fuel cell subassembly of embodiment 1,        wherein the electrode layer is disposed between a first surface        of an electrolyte membrane and a first gas diffusion layer, the        fuel cell subassembly further comprising additional components        of a membrane electrode assembly (MEA) including a second        electrode layer disposed between a second surface of the        electrolyte membrane and a second gas diffusion layer.        Embodiment 20 is the fuel cell subassembly of embodiment 19,        further comprising:

a first flow field plate disposed proximate the first gas diffusionlayer; and

a second flow field plate disposed proximate the second gas diffusionlayer.

Embodiment 21 is the fuel cell subassembly of embodiment 19, furthercomprising multiple MEAs arranged to form a fuel cell stack.Embodiment 22 is a method of making a fuel cell electrode layer,comprising:

combining an ionic conductor, an electronic conductor, a catalyst, and asolvent, the ionic conductor comprising spheroid particles, a majorityof the particles having diameters greater than about 50 nm;

mixing the ionic conductor, the electronic conductor, the catalyst andthe solvent for a period of time to form an electrode ink; and

coating the electrode ink on a substrate to form the fuel cell electrodelayer.

Embodiment 23 is the method of embodiment 22, wherein a majority of theparticles have a diameter greater than about 1 μm.Embodiment 24 is the method of embodiment 22, wherein the particles havea diameter range between about 50 nm to about 15 μm.Embodiment 25 is the method of embodiment 22, wherein the electronicconductor is coated with the catalyst.Embodiment 26 is the method of embodiment 22, wherein the catalystdisposed on support structures.Embodiment 27 is the method of embodiment 22, wherein the catalyst isdisposed on nanostructured supports.Embodiment 28 is the method of embodiment 22, wherein the substratecomprises an electrolyte membrane.Embodiment 29 is the method of embodiment 22, wherein the substratecomprises a gas diffusion layer.Embodiment 30 is the method of embodiment 22, wherein the particlescomprise spray dried ionomer particles.Embodiment 31 is the method of embodiment 22, wherein a majority of theparticles are spheroids.Embodiment 32 is the method of embodiment 22, wherein a majority of theparticles have a substantially smooth surface.Embodiment 33 is the method of embodiment 22, wherein a majority of theparticles are hollow.Embodiment 34 is the method of embodiment 22, wherein combining theionic conductor, the electronic conductor, the catalyst and the solventcomprises substantially contemporaneously combining the ionic conductor,the electronic conductor, and the solvent prior to the mixing.Embodiment 35 is the method of embodiment 22, wherein combining theionic conductor, the electronic conductor, the catalyst and the solventcomprises:

forming a pre-mixture that includes the electronic conductor and thesolvent;

mixing the pre-mixture for a period of time;

after mixing the pre-mixture, adding the ionic conductor to thepre-mixture; and

mixing the ionic conductor and the pre-mixture for a period of time.

Embodiment 36 is the method of embodiment 22, further comprising aftermixing the ionic conductor, the electronic conductor, and the solvent,adding a second type of ionic conductor with the mixture of the ionicconductor, the electronic conductor, and the solvent.Embodiment 37 is the method of embodiment 22, wherein the ionicconductor comprises a first type of ion conducting polymer and a secondtype of ion conducting polymer.Embodiment 38 is the method of embodiment 22, wherein the ionicconductor comprises a first form of an ion conducting polymer and asecond form of the ion conducting polymer.Embodiment 39 is the method of embodiment 22, wherein the ionicconductor comprises a first equivalent weight ionic conductor and asecond equivalent weight ionic conductor.Embodiment 40 is the method of embodiment 22, wherein the ionicconductor comprises:

particles of a first ion conducting polymer, a majority of the particlesof the first ion conducting polymer having diameters greater than about1 μm; and

particles of a second ion conducting polymer, a majority of theparticles of the second ion conducting polymer having diameters lessthan about 50 nm.

Embodiment 41 is the method of embodiment 40, wherein a volume of thefirst ion conducting polymer is greater that a volume of the second ionconducting polymer.Embodiment 42 is the method of embodiment 41, wherein the particles ofthe second ion conducting polymer coat the electronic conductor.Embodiment 43 is the method of embodiment 22, further comprising formingthe ionic conductor by spray drying an ion conducting polymer.Embodiment 44 is the method of embodiment 43, wherein forming the ionicconductor by spray drying the ion conducting polymer comprises adding anadditive to the ion conducting polymer prior to or during the spraydrying.Embodiment 45 is the method of embodiment 44, wherein the additivecomprises one or more of cerium and manganese compounds.Embodiment 46 is the method of embodiment 22, wherein combiningcomprises one or more of ball mixing, stirring, and sonication.Embodiment 47 is the method of embodiment 22, wherein the solventcomprises one or more of a hydrocarbon and water.Embodiment 48 is a fuel cell subassembly, comprising:

an electrode layer, comprising:

-   -   a catalyst;    -   an electronic conductor;    -   an ionic conductor intermixed with the electronic conductor and        the catalyst and comprising particles, a majority of the        particles being spheroid particles having diameters greater than        about 50 nm.        Embodiment 49 is the fuel cell subassembly of embodiment 48,        wherein a majority of the particles of the ionic conductor have        a substantially smooth outer surface.        Embodiment 50 is the fuel cell subassembly of embodiment 48,        wherein a majority of the particles are hollow.        Embodiment 51 is the fuel cell subassembly of embodiment 48,        wherein a majority of the particles have diameters in a range of        about 1 μm to about 15 μm.        Embodiment 52 is the fuel cell subassembly of embodiment 48,        wherein the catalyst is disposed on the electronic conductor.        Embodiment 53 is the fuel cell subassembly of embodiment 48,        wherein the catalyst is disposed on nanostructured supports.        Embodiment 55 is the fuel cell subassembly of embodiment 48,        wherein the ionic conductor comprises one or more of        perfluorinated sulfonic acid and perfluorinated imide acid.        Embodiment 56 is the fuel cell subassembly of embodiment 48,        further comprising a second ionic conductor.        Embodiment 57 is the fuel cell subassembly of embodiment 56,        wherein the ionic conductor has a first equivalent weight and        the second ionic conductor has a second equivalent weight.        Embodiment 58 is the fuel cell subassembly of embodiment 56,        wherein the second ionic conductor comprises particles, and a        majority of the particles of the second ionic conductor have        diameters less than about 50 nm.        Embodiment 59 is the fuel cell subassembly of embodiment 48,        wherein a majority of the particles of the ionic conductor are        non-uniformly distributed within the electrode layer.        Embodiment 60 is the fuel cell subassembly of embodiment 48,        wherein the electrode layer is disposed on an electrolyte        membrane.        Embodiment 61 is the fuel cell subassembly of embodiment 48,        wherein the electrode layer is disposed on a gas diffusion        layer.        Embodiment 62 is the fuel cell subassembly of embodiment 48,        wherein the electrode layer is disposed between a first surface        of an electrolyte membrane and a first gas diffusion layer, the        fuel cell subassembly further comprising additional components        of a membrane electrode assembly (MEA) including a second        electrode layer disposed between a second surface of the        electrolyte membrane and a second gas diffusion layer.        Embodiment 63 is the fuel cell subassembly of embodiment 62,        further comprising:

a first flow field plate disposed proximate the first gas diffusionlayer; and

a second flow field plate disposed proximate the second gas diffusionlayer.

Embodiment 64 is the fuel cell subassembly of embodiment 62, furthercomprising multiple MEAs arranged to form a fuel cell stack.Embodiment 65 is a fuel cell electrode layer, comprising:

a catalyst;

an electronic conductor; and

a first ionic conductor; and

a second ionic conductor, wherein the first ionic conductor is differentfrom the second ionic conductor and the first ionic conductor and thesecond ionic conductor are interspersed with each other, the electronicconductor, and the catalyst within the electrode layer.

Embodiment 66 is the electrode layer of embodiment 65, wherein the firstionic conductor and the second ionic conductor are different types ofionic conductor.Embodiment 67 is the electrode layer of embodiment 65, wherein the firstionic conductor and the second ionic conductor are different forms ofthe same type of ionic conductor.Embodiment 68 is the electrode layer of embodiment 65, wherein the firstionic conductor has a first equivalent weight and the second ionicconductor has a second equivalent weight.Embodiment 69 is the electrode layer of embodiment 65, wherein particlesof the second ionic conductor coat the electronic conductor.Embodiment 70 is the electrode layer of embodiment 65, wherein particlesof the second ionic conductor are substantially smaller than particlesof the first ionic conductor.Embodiment 71 is the electrode layer of embodiment 65, wherein amajority of particles of the second ionic conductor have diameters lessthan about 50 nm and particles of the first ionic conductor are powderedspray dried particles or powdered cryoground particles.Embodiment 72 is the electrode layer of embodiment 65, wherein particlesof one or both of the first ionic conductor and the second ionicconductor are non-uniformly distributed in the electrode layer.Embodiment 73 is the fuel cell subassembly of embodiment 1, wherein theionic conductor comprises particles and a majority of the particles havediameters in a range of 1 μm to 15 μm.Embodiment 74 is the fuel cell subassembly of embodiment 1, wherein theionic conductor comprises particles and a majority of the particles havediameters in a range of 1.5 μm to 14 μm.Embodiment 75 is the fuel cell subassembly of embodiment 1, wherein theionic conductor comprises particles and a majority of the particles havediameters in a range of 2 μm to 12 μm.Embodiment 76 is the fuel cell subassembly of embodiment 12, wherein:

-   -   the first ion conducting polymer comprises particles, and a        majority of the particles of the first ion conducting polymer        have diameters greater than 1 μm; and    -   the second ion conducting polymer comprises particles, and a        majority of the particles of the second ion conducting polymer        have diameters less than 50 nm.        Embodiment 77 is the fuel cell subassembly of embodiment 12,        wherein:    -   the first ion conducting polymer comprises particles, and a        majority of the particles of the first ion conducting polymer        have diameters greater than 1.5 μm; and    -   the second ion conducting polymer comprises particles, and a        majority of the particles of the second ion conducting polymer        have diameters less than 50 nm.        Embodiment 78 is the fuel cell subassembly of embodiment 12,        wherein:    -   the first ion conducting polymer comprises particles, and a        majority of the particles of the first ion conducting polymer        have diameters greater than 1 μm; and    -   the second ion conducting polymer comprises particles, and a        majority of the particles of the second ion conducting polymer        have diameters less than 40 nm.        Embodiment 79 is the fuel cell subassembly of embodiment 12,        wherein:    -   the first ion conducting polymer comprises particles, and a        majority of the particles of the first ion conducting polymer        have diameters greater than 1.5 μm; and    -   the second ion conducting polymer comprises particles, and a        majority of the particles of the second ion conducting polymer        have diameters less than 40 nm.        Embodiment 80 is the method of embodiment 22, wherein a majority        of the particles have a diameter greater than 50 nm.        Embodiment 81 is the method of embodiment 22, wherein a majority        of the particles have a diameter greater than 75 nm.        Embodiment 82 is the method of embodiment 22, wherein a majority        of the particles have a diameter greater than 1 μm.        Embodiment 83 is the method of embodiment 22, wherein a majority        of the particles have a diameter greater than 1.5 μm.        Embodiment 84 is the method of embodiment 22, wherein the        particles have a diameter range between 50 nm to 15 μm.        Embodiment 85 is the method of embodiment 22, wherein the        particles have a diameter range between 50 nm to 12 μm.        Embodiment 86 is the method of embodiment 22, wherein the        particles have a diameter range between 75 nm to 12 μm.        Embodiment 87 is the method of embodiment 22, wherein the        particles have a diameter range between 1 μm to 12 μm.        Embodiment 88 is the method of embodiment 22, wherein the        particles have a diameter range between 1.5 μm to 12 μm.        Embodiment 89 is the method of embodiment 22, wherein the ionic        conductor comprises:

particles of a first ion conducting polymer, a majority of the particlesof the first ion conducting polymer having diameters greater than 1 μm;and

particles of a second ion conducting polymer, a majority of theparticles of the second ion conducting polymer having diameters lessthan 50 nm.

Embodiment 90 is the method of embodiment 22, wherein the ionicconductor comprises:

particles of a first ion conducting polymer, a majority of the particlesof the first ion conducting polymer having diameters greater than 1.5μm; and

particles of a second ion conducting polymer, a majority of theparticles of the second ion conducting polymer having diameters lessthan 50 nm.Embodiment 91 is the method of embodiment 22, wherein the ionicconductor comprises:

particles of a first ion conducting polymer, a majority of the particlesof the first ion conducting polymer having diameters greater than 1 μm;and

particles of a second ion conducting polymer, a majority of theparticles of the second ion conducting polymer having diameters lessthan 40 nm.Embodiment 92 is the method of embodiment 22, wherein the ionicconductor comprises:

particles of a first ion conducting polymer, a majority of the particlesof the first ion conducting polymer having diameters greater than 1.5μm; and

particles of a second ion conducting polymer, a majority of theparticles of the second ion conducting polymer having diameters lessthan 40 nm.Embodiment 93 is the fuel cell subassembly of embodiment 48, wherein amajority of the particles have diameters in a range of 1 μm to 15 μm.Embodiment 94 is the fuel cell subassembly of embodiment 48, wherein amajority of the particles have diameters in a range of 1.5 μm to 15 μm.Embodiment 95 is the fuel cell subassembly of embodiment 48, wherein amajority of the particles have diameters in a range of 1 μm to 12 μm.Embodiment 96 is the fuel cell subassembly of embodiment 48, wherein amajority of the particles have diameters in a range of 1.5 μm to 12 μm.Embodiment 97 is the fuel cell subassembly of embodiment 56, wherein thesecond ionic conductor comprises particles, and a majority of theparticles of the second ionic conductor have diameters less than 50 nm.Embodiment 98 is the fuel cell subassembly of embodiment 56, wherein thesecond ionic conductor comprises particles, and a majority of theparticles of the second ionic conductor have diameters less than 40 nm.Embodiment 99 is the fuel cell subassembly of embodiment 56, wherein amajority of the particles have diameters in a range of 1 μm to 15 μm,wherein the second ionic conductor comprises particles, and wherein amajority of the particles of the second ionic conductor have diametersless than 50 nm.Embodiment 100 is the fuel cell subassembly of embodiment 56, wherein amajority of the particles have diameters in a range of 1 μm to 15 μm,wherein the second ionic conductor comprises particles, and wherein amajority of the particles of the second ionic conductor have diametersless than 40 nm.Embodiment 101 is the method of embodiment 22, wherein at least 10% ofthe particles are hollow.Embodiment 102 is the method of embodiment 22, wherein at least 20% ofthe particles are hollow.Embodiment 103 is the method of embodiment 22, wherein at least 30% ofthe particles are hollow.Embodiment 104 is the method of embodiment 22, wherein at least 40% ofthe particles are hollow.

The foregoing description of the various examples and embodiments hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseforms disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope be limited not bythis detailed description, but rather by the claims appended hereto.

1. A fuel cell subassembly, comprising: an electrode layer, comprising: a catalyst; an electronic conductor; an ionic conductor; a plurality of electronic conductor rich networks within the electrode layer; and a plurality of ionic conductor rich networks within the electrode layer and interspersed with the electronic conductor rich networks, wherein a volume ratio of the ionic conductor to the electronic conductor is greater in the ionic conductor rich networks than in the electronic conductor rich networks.
 2. The fuel cell subassembly of claim 1, wherein the ionic conductor comprises particles of a spray dried ion conducting polymer.
 3. The fuel cell subassembly of claim 1, wherein the ionic conductor comprises particles and a majority of the particles are substantially smooth, spheroid, and have diameters in a range of about 1 μm to about 15 μm.
 4. The fuel cell subassembly of claim 1, wherein the electrode layer further comprises a second ionic conductor, wherein the ionic conductor has a first equivalent weight and the second ionic conductor has a second equivalent weight.
 5. A method of making a fuel cell electrode layer, comprising: combining an ionic conductor, an electronic conductor, a catalyst, and a solvent, the ionic conductor comprising spheroid particles, a majority of the spheroid particles having substantially smooth outer surfaces and having diameters greater than about 50 nm; mixing the ionic conductor, the electronic conductor, the catalyst and the solvent for a period of time to form an electrode ink; and coating the electrode ink on a substrate to form the fuel cell electrode layer.
 6. The method of claim 5, wherein a majority of the particles have a diameter greater than about 1 μm.
 7. The method of claim 5, wherein the particles comprise spray dried ionomer particles.
 8. The method of claim 5, wherein a majority of the particles are hollow.
 9. The method of claim 5, wherein the ionic conductor comprises a first type of ion conducting polymer and a second type of ion conducting polymer.
 10. The method of claim 5, further comprising combining a second ionic conductor in the electrode ink.
 11. The method of claim 10, wherein the second ionic conductor comprises particles, and a majority of the particles of the second ionic conductor have a diameter less than about 50 nm.
 12. A fuel cell subassembly, comprising: an electrode layer, comprising: a catalyst; an electronic conductor; an ionic conductor intermixed with the electronic conductor and the catalyst and comprising particles, a majority of the particles of the ionic conductor being spheroid particles having a diameter greater than about 50 nm.
 13. The fuel cell subassembly of claim 12, wherein a majority of the particles of the ionic conductor have a substantially smooth outer surface.
 14. The fuel cell subassembly of claim 12, wherein a majority of the particles are hollow.
 15. The fuel cell subassembly of claim 12, wherein a majority of the particles have diameters in a range of about 1 μm to about 15 μm.
 16. The fuel cell subassembly of claim 12, wherein a majority of the particles are spray dried powdered ion conducting polymer particles.
 17. The fuel cell subassembly of claim 12, wherein the particles are non-uniformly distributed in the electrode layer.
 18. A fuel cell electrode layer, comprising: a catalyst; an electronic conductor; and a first ionic conductor; and a second ionic conductor, wherein the first ionic conductor is different from the second ionic conductor and the first ionic conductor and the second ionic conductor are interspersed with each other, the electronic conductor, and the catalyst within the electrode layer.
 19. The electrode layer of claim 18, wherein the first ionic conductor and the second ionic conductor are different types of ionic conductor.
 20. The electrode layer of claim 18, wherein the first ionic conductor and the second ionic conductor are different forms of the same type of ionic conductor.
 21. The electrode layer of claim 18, wherein the first ionic conductor has a first equivalent weight and the second ionic conductor has a second equivalent weight.
 22. The electrode layer of claim 18, wherein a majority of the particles of the first ionic conductor have a diameter greater than about 1 μm and a majority of the particles of the second ionic conductor have a diameter less than about 50 nm.
 23. The electrode layer of claim 18, wherein the first ionic conductor comprises particles, and a majority of the particles of the first ionic conductor are substantially smooth and hollow.
 24. The electrode layer of claim 18, wherein a majority of particles of the first ionic conductor are powdered spray dried particles or powdered cryoground particles.
 25. The electrode layer of claim 18, wherein particles of the first ionic conductor are non-uniformly distributed in the electrode layer and particles of the second ionic conductor coat the electronic conductor. 